It is normal for various detectors to be present in the piping systems associated with a chromatography column, either immediately adjacent or on the column, or in associated machinery such as packing skids which may from time to time be connected to the column. For example it is normal for the outflow from the column to include a pH meter and/or a UV monitor, the latter detecting the presence of chemical species in the outflow which have UV-absorptive chromophores. Normally a pressure gauge is connected to the column interior or pumping system.
In the prior-published art, U.S. Pat. No. 4,324,131 describes using a ultrasonic detector to detect solutes in the effluent liquid from a chromatography column; only schematic details are given but essentially ultrasound is passed through a cell through which the effluent passes and a second, control cell containing pure eluent; differences in the transmitted ultrasound amplitude indicate dissolved substances.
Our earlier but not prior-published WO 02/10739, the contents of which are hereby incorporated by reference, describes a different mode of use of ultrasound in relation to chromatography columns and processes. It is disclosed that vibratory transmissions, especially ultrasound, can pass right across the packed column interior and indicate the situation within. A particular aspect is showing the presence of absence of packed bed material (medium); various methods and apparatus are disclosed for using ultrasound arrangements to monitor and control the packing of a column. It was also found that the ultrasound transmissions can detect the presence of additional substances in the column, in particular bands of eluted components passing through, and bound impurities or other components remaining in a band on the media so as to affect the ultrasound transmission.